1. Field of the Invention
The present invention relates to a copying apparatus provided with an automatic document feeder capable of serially placing a pair of original documents at a specified position on a platen, and discharging them from the platen after the completion of exposure.
2. Description of the Prior Art
To reduce a time for replacing original documents or to eliminate type procedure for the document replacement, various copying apparatuses provided with an automatic document feeder (hereinafter abbreviated as ADF) have been recently developed and commercially available. Such an ADF constitutes means for reducing indirect costs (time and labor). In contrast, to reduce direct costs (supplies, such as copy sheets and toner), several methods available are as follows: a duplex copying method, wherein two documents are copied to both sides of one copy sheet; and a method for reducing and copying two documents to one side of a copy sheet having the same size as each original document (two-document, single-face copying mode). In the former method, a pair of documents are unchangedly copied to one side of a copy sheet, while toner making for two copies is consumed. In contrast, the latter method is economical in that a copy sheet and toner each for only one sheet of document is consumed per two duplicates. Furthermore, when the above two methods combined, the result is extreme economization, since four documents are copied using both sides of one copy sheet.
Various conventional ADFs, however, feed documents one by one onto a platen. Accordingly, to perform two-document, one side copying, an operator is supposed to replace documents and place them on the platen per sheet of document, thus time and labor are not reduced.
To solve such disadvantages, for example, an ADF for feeding two documents serially onto a platen in the direction of the document feeding has been disclosed in Japanese Patent Laid Open Publication Nos. 60-2942, 60-84945 and 60-93452. A copying machine provided with this type of ADF, however, has the following disadvantages. When a dual document feeding mode is selected, if the sizes of a first and second documents is different, a blank is inevitably formed on a copy sheet when these two documents are copied on one sheet, regardless of the magnification designated. In the same way, if at least one of the two documents is longitudinal orientation i.e. the longer side thereof has been set in the document feeding direction, or is longer than the half of the platen, this is, the entire exposure area (document image scanning area with an optical system), the total length of the two documents may exceed the entire exposure area, upon placing them on the platen. In this case, images of the two documents are not properly formed on one copy sheet no matter what magnification has been specified, resulting in an incomplete duplicate with a part of image missing. Although the images of the two documents may duplicate on one sheet, a blank is inevitably formed on the sheet.
As for the document size, the ADF disclosed in said Japanese Patent Laid Open Publication No. 60-93462 is known in the art, wherein an operator can select a relevant document size by select means on a control panel, from the following three document size types: the first size where two documents can be set on the platen, such as in the case of latitudinal positioned A4 size, B5 size, letter size and A5 size: the second size where the documents are placed on the platen so that the longer sides of the documents are set in the document feeding direction, such as in the case of longitudinal positioned A4 size and B5 size; and third size in which only one document is set on the platen, such as in the case of A3 size, B4 size, legal size and leisure size. Yet such document size selection is complicated of the part of an operator, thus an accident mis-copying cannot be positively prevented.